1. Field of the Invention
The present invention relates to a pulsar ring which serves as a detected part of a rotation speed sensor used for ABS or the like of cars, a magnetizing device and a magnetizing method used for applying a magnetized member having a number of magnetic poles alternately formed thereon to the pulsar ring, and a bearing unit having a bearing on which the pulsar ring and the sensor are installed.
2. Description of the Related Art
In railway vehicles and cars, a antifriction bearing unit with a sensor, which has a antifriction bearing, a sensor device attached thereto and a pulsar ring serving as a detected part, has been used for supporting a vehicle shaft or a rotary shaft for transmitting rotations to the vehicle shaft and for detecting the rotation speed of the shaft.
Pulsar rings are classified into those of a gear type that are manufactured by machining or the like, and those of a magnetic type that are manufactured by using molds, and the dimension and shape thereof are determined depending on the dimension and shape of a antifriction bearing to which the pulsar ring is attached.
The pulsar ring of the magnetic type is formed by bonding a rubber magnetic material (formed by dispersing magnetic material powder in rubber) to a circumferential surface of a ring-shaped supporting member that has been manufactured so as to be applied to the bearing, and by magnetizing the rubber magnetic material by using a magnetizing-use mold that has been manufactured in accordance with the dimensions of the supporting member and the rubber magnetic material.
In the conventional magnetic pulsar ring, it is necessary to manufacture a new magnetizing-use mold each time the bearing is modified, resulting in high costs.
Examples of the magnetizing device for the pulsar ring-use magnetized member include a multipolar magnetizing device which simultaneously magnetizes a number of magnetic poles and a single-polar magnetizing device which magnetizes pole by pole while shifting the member to be magnetized. In the conventional multipolar magnetizing device, a magnetizing process is carried out on one surface of a member to be magnetized with the member to be magnetized being supported on a supporting member; consequently, although this process has an advantage in that the magnetizing process is carried out at one time, the resulting magnetic force is weak, causing a difficulty in sensing the change in its magnetic characteristic by using a magnetic sensor. In order to solve this problem, the size of a current used for magnetizing is increased, and the sensitivity of the magnetic sensor is increased; however, the former has a problem of high costs required for magnetizing, and the latter has a problem of an expensive magnetic sensor.
Moreover, in the conventional bearing unit with a sensor in which the above-mentioned pulsar ring is provided on a bearing together with a sensor device, magnetic poles are formed with equal pitches so as to continuously provide an uniform output in the pulsar ring, with the result that it is not possible to find an origin signal serving as a reference for one rotation. Therefore, in order to detect an absolute angle based upon the origin, an origin detecting sensor and an origin detecting ring (or a detected point) are required, resulting in a complex mechanical structure and a new space in which these parts are assembled.